Editor's note: Book rental startup Chegg is making money hand over fist. Guest author Steven Carpenter does a teardown of its business model and estimates its revenues will reach $130 million this year. Carpenter was the founder and CEO of Cake Financial , which was sold to E*Trade earlier this year. Previously, he's written TC Teardowns on Groupon and Zynga . Chegg may very well be the fastest-growing, most successful, second-generation e-commerce startup that you hardly ever hear about,except maybe for the fact that it's raised more than $140 million. Chegg is the “Netflix for textbooks." It lets students across 6,400 college campuses rent from a virtual bookstore containing 4.2 million books. Based on my analysis (which I get into more detail below), the company is on track to generate $130 million in revenues in 2010, up from $25 million in 2009, and $10 million in 2008. During the January, 2010 semester, I estimate the company made close to $1 million in revenue a day, up fivefold from $200,000/day the previous January, and it should double that this coming September. My analysis suggests Chegg will do close to $50 million in revenue this September alone. It is underappreciated, to say the least.